In general, activities that involve impacts with the earth, such as running and jumping, are the most effective way to improve bone health, according to Dr. Jon Tobias, a professor of rheumatology at the University of Bristol who studies bone health. They create ground-reaction forces that move through your bones and stimulate them to “remodel” themselves and add density, he said. They also entail strong muscular contractions that tug at and slightly bend attached bones, redoubling the stimulating effects of the exercise.
Sprinting and hopping are the most obvious and well-studied examples of high-impact exercises. In one recent study, women ages 25 to 50 who leaped like fleas at least 10 times in a row, twice per day for four months, significantly increased the density of their hipbones. In another, more elaborate experiment from 2006, women who hopped and also lifted weights improved the density of their spines by about 2 percent compared to a control group, especially if the weight training targeted both the upper body and the legs. Women whose weight training focused only on the legs did not gain as much density in their spines.